靠模车削机构为（）凸轮机构。
A.盘形
B.板状
C.圆柱
D.圆锥
参考答案：B
The l9th century ___ the greatest number of laws stopping the rights and progress of the black. [ ]
A. witnesses
B. is witnessing
C. witnessed
D. has witnessed
6个千，6个千分之一组成的数是______．
